1. Field of the Invention
The invention relates to an insulating coating material and an insulated wire using the insulating coating material, in particular, to an insulating coating material that pseudoplasticity is imparted to a polyamide-imide resin insulating coating material, and an insulated wire using the insulating coating material.
2. Description of the Related Art
A rectangular enameled wire composed of a conductor having a rectangular cross section (rectangular conductor) and an insulating layer formed thereon by applying and baking an insulating coating material is desired to have characteristics as an insulated wire, such as flexibility, abrasion resistance and softening resistance, etc., and also to have a the insulation layer which is formed to have a uniform thickness throughout the entire circumference of the conductor so as not to have thin portions in light of electrical characteristics, etc.
In order to facilitate uniform coating on a conductor having a circular cross section, an insulating coating material used for an enameled wire, such as a polyamide-imide resin insulating coating material, is generally adjusted to have a relatively low viscosity so as not to inhibit the effect of surface tension by which the insulating coating material makes a shape having a circular cross section on the conductor. On the other hand, the higher the viscosity of the insulating coating material, the smaller the surface tension effect of the insulating layer and also the longer it takes to become a shape having a circular cross section, hence, the insulating coating material on the conductor keeps a shape of a coating die.
A coating technology to reduce a film thickness per coating application is attempted to uniformly apply an existing polyamide-imide resin insulating coating material to a rectangular conductor, however, it requires many coating applications to have a thick coating and the thicker coating has more remarkable unevenness in thickness. Meanwhile, although a technique of applying a hydrosoluble polymer, etc., by electrodeposition coating is known, this technique is to address thin film coatings and has a difficulty to coat a thick insulating layer (e.g., coating of not less than 20 μm in a thickness).
As described above, although improvement in a coating technique has been sought to address the demand for uniform application of polyamide-imide resin insulating coating material on a rectangular conductor, coating materials have not been improved yet.
Patent Literatures
Patent Literature 1: JP-A-2004-339251, Patent Literature 2: WO 2006/098409, Patent Literature 3: JP-A-2007-141507, Patent Literature 4: JP-A-2008-257925, Patent Literature 5: JP-A-2006-302835, Patent Literature 6: Japanese patent No. 4177295